A nuclear weapons test is an attempt to cause one or more nuclear explosions in devices in a close proximity in space and time; the standard definition used in treaty language for the space/time requirement is:

In conformity with treaties between the United States and the Soviet Union, a salvo is defined, for multiple explosions for peaceful purposes, as two or more separate explosions where a period of time between successive individual explosions does not exceed 5 seconds and where the burial points of all explosive devices can be connected by segments of straight lines, each of them connecting two burial points, and the total length does not exceed 40 kilometers. For nuclear weapon tests, a salvo is defined as two or more underground nuclear explosions conducted at a test site within an area delineated by a circle having a diameter of two kilometers and conducted within a total period of time of 0.1 second.[1]

This definition is inclusive of zero-yield safety tests, whether there is a nuclear yield (the test is unsuccessful) or not. It does not include hydronuclear, cold or subcritical tests because no nuclear explosions are intended. In these sorts of tests there may be small amounts of chain reaction occurring, but they stop before materially adding to the chemical explosion that causes them. The line here is finely drawn, but, among other things, subcritical testing is not prohibited by the Comprehensive Nuclear Test Ban Treaty, while safety tests are.[2][3]

The table in this section summarizes all worldwide nuclear testing (including the two bombs dropped in combat which were not tests). The country names are links to summary articles for each country, which may in turn be used to drill down to test series articles which contain details on every known nuclear explosion and test. The notes attached to various table cells detail how the numbers therein are arrived at. As of 1993, worldwide, 520 atmospheric nuclear explosions (including 8 underwater) have been conducted with a total yield of 545 Megaton (Mt): 217 Mt from fission and 328 Mt from fusion, while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions with a total yield of 90 Mt.[4]

The standard "official" list of tests for American devices is arguably the United States Department of Energy DoE-209 document.[5] The United States conducted around 1,054 nuclear tests (by official count) between 1945 and 1992, including 216 atmospheric, underwater, and space tests.[9] Some significant tests conducted by the United States include:[10]

The Ivy Mike shot of 1 November 1952, was the first full test of a Teller-Ulam design "staged" hydrogen bomb, with a yield of 10 megatons. This was not a deployable weapon: With its full cryogenic equipment it weighed some 82 tons.

The Castle Bravo shot of 1 March 1954, was the first test of a deployable (solid fuel) thermonuclear weapon, and also (accidentally) the largest weapon ever tested by the United States (15 megatons). It was also the single largest U.S. radiological accident in connection with nuclear testing. The unanticipated yield, and a change in the weather, resulted in nuclear fallout spreading eastward onto the inhabited Rongelap and Rongerik atolls, which were soon evacuated. Many of the Marshall Islands natives have since suffered from birth defects and have received some compensation from the federal government. A Japanese fishing boat, the Fifth Lucky Dragon, also came into contact with the fallout, which caused many of the crew to grow ill; one eventually died. The crew's exposure was referenced in the film Godzilla as a criticism of American nuclear tests in the Pacific.

Shot Frigate Bird of Operation Dominic on 6 May 1962, was the only U.S. test of an operational ballistic missile with a live nuclear warhead (yield of 600 kilotons), at Kiritimati (formerly Christmas Island) in the Pacific. In general, missile systems were tested without live warheads and warheads were tested separately for safety concerns. In the early 1960s there were mounting questions about how the systems would behave under combat conditions (when they were "mated", in military parlance), and this test was meant to dispel these concerns. However, the warhead had to be somewhat modified before its use, and the missile was only a SLBM (and not an ICBM), so by itself it did not satisfy all concerns.[11]

Shot Sedan of Operation Storax on 6 July 1962 (yield of 104 kilotons), was an attempt at showing the feasibility of using nuclear weapons for civilian, peaceful purposes as part of Operation Plowshare. In this instance, a 1280-feet-in-diameter and 320-feet-deep explosion crater, morphologically similar to an impact crater, was created at the Nevada Test Site.

After the fall of the USSR, the American government (as a member of the International Consortium "International Science and Technology Center", http://www.istc.ru) hired a number of top scientists in Sarov (aka Arzamas-16, the Soviet equivalent of Los Alamos and thus sometimes called "Los Arzamas") to draft a number of documents about the history of the Soviet atomic program.[13] One of the documents was the definitive list of Soviet nuclear tests.[6] Most of the tests have no code names, unlike the American tests, so they are known by their test numbers from this document. Some list compilers have detected discrepancies in that list; one device was abandoned in its cove in a tunnel in Semipalatinsk when the Soviets abandoned Kazakhstan,[14] and one list[15] lists 13 other tests which apparently failed to provide any yield. The source for that was the well respected Russian Strategic Nuclear Forces[7] which confirms 11 of the 13; those 11 are in the Wikipedia lists.

RDS-6s (known as Joe 4 in the West), August 12, 1953: first Soviet thermonuclear test using a sloika (layer cake) design. The design proved to be unscalable into megaton yields, but it was air-deployable.

The last Soviet test took place on October 24, 1990. After the dissolution of the USSR in 1992, Russia inherited the USSR's nuclear stockpile, while Kazakhstan inherited the Semipalatinsk nuclear test area, as well as the Baikonur Cosmodrome, the Sary Shagan missile/radar test area and three ballistic missile fields. Semipalatinsk included at least the one unexploded device, later blown up with conventional explosives by a combined USA/Kazakh team. No testing has occurred in the former territory of the USSR since its dissolution.

The United Kingdom has conducted 45 tests (21 in Australian territory, including 9 in mainland South Australia at Maralinga and Emu Field, 3 at Malden Island and 6 at Kiritibati (Christmas Island) in the Line Islands of the central Pacific, and 24 in the U.S. as part of joint test series). Often excluded from British totals are the 31 safety tests of Operation Vixen in Maralinga. British test series include:

Operation Gerboise bleue, February 13, 1960 (first atomic bomb) and three more: Reggane, Algeria; in the atmosphere; final test reputed to be more intended to prevent the weapon from falling into the hands of generals rebelling against French colonial rule than for testing purposes.[20]

The foremost list of Chinese tests compiled by the Federation of American Scientists[21] skips over two Chinese tests listed by others. The People's Republic of China conducted 45 tests (23 atmospheric and 22 underground, all conducted at Lop Nur Nuclear Weapons Test Base, in Malan, Xinjiang)

India announced it had conducted a test of a single device in 1974 near Pakistan's eastern border under the codename Operation Smiling Buddha. After 24 years, India publicly announced five further nuclear tests on May 11 and May 13, 1998. The official number of Indian nuclear tests is six, conducted under two different code-names and at different times.

May 11, 1998: Operation Shakti (type: implosion, 3 uranium and 2 plutonium devices, all underground). The Atomic Energy Commission (AEC) of India and the Defence Research and Development Organisation (DRDO) simultaneously conducted a test of three nuclear devices at the Indian ArmyPokhran Test Range (IAPTR) on May 11, 1998. Two days later, on May 13, the AEC and DRDO carried out a test of two further nuclear devices, detonated simultaneously. During this operation, AEC India claimed to have tested a three-stage thermonuclear device (Teller-Ulam design), but the yield of the tests was significantly lower than that expected from thermonuclear devices. The yields remain questionable, at best, by Western and Indian scholars, estimated at 20kt-45kt.

Pakistan conducted 6 official tests, under 2 different code names, in the final week of May 1998. From 1983 to 1994, around 24 nuclear cold tests were carried out by Pakistan; these remained unannounced and classified until 2000. In May 1998, Pakistan responded publicly by testing 6 nuclear devices.[26]

May 28, 1998: Chagai-I (type: implosion, HEU and underground). One underground horizontal-shaft tunnel test (inside a granite mountain) of boosted fission devices at Koh Kambaran in the Ras Koh Hills in Chagai District of Balochistan Province.[26][28] The announced yield of the five devices was a total of 40–45 kilotonnes with the largest having a yield of approximately 30–45 kilotonnes. An independent assessment however put the test yield at no more than 12 kt and the maximum yield of a single device at only 9 kt as opposed to 35 kt as claimed by Pakistani authorities.[29] According to The Bulletin of the Atomic Scientists, the maximum yield was only 2–10 kt as opposed to the claim of 35 kt and the total yield of all tests was no more than 8–15 kt.[30]

May 30, 1998: Chagai-II (type: implosion, plutonium device and underground). One underground vertical-shaft tunnel test of a miniaturized fission device having an announced yield of approximately 18–20 kilotonnes, carried out in the Kharan Desert in Kharan District, Balochistan Province.[28] An independent assessment put the figure of this test at 4–6 kt only.[29] Some Western seismologists put the figure at a mere 2 kt.[30]

On October 9, 2006, North Korea announced they had conducted a nuclear test in North Hamgyong Province on the northeast coast at 10:36 AM (11:30 AEST). There was a 3.58 magnitude earthquake reported in South Korea. There was a 4.2 magnitude tremor detected 240 miles north of P'yongyang. The low estimates on the yield of the test—potentially less than a kiloton in strength—have led to speculation as to whether it was a fizzle (unsuccessful test), or not a genuine nuclear test at all.

On May 25, 2009, North Korea announced having conducted a second nuclear test. A tremor, with magnitude reports ranging from 4.7 to 5.3, was detected at Mantapsan, 233 miles northeast of P'yongyang and within a few kilometers of the 2006 test location. While estimates as to yield are still uncertain, with reports ranging from 3 to 20 kilotons, the stronger tremor indicates a significantly larger yield than the 2006 test.

There have been a number of significant alleged/disputed/unacknowledged accounts of countries testing nuclear explosives. Their status is either not certain or entirely disputed by most mainstream experts.

Because Pakistan's nuclear programme was conducted under extreme secrecy, it raised concerns in the Soviet Union and India, who suspected that since the 1974 test it was inevitable that Pakistan would further develop its programme. The pro-Soviet newspaper, The Patriot, reported that "Pakistan has exploded a nuclear device in the range of 20 to 50 kilotons" in 1983.[38] But it was widely dismissed by Western diplomats as it was pointed out that The Patriot had previously engaged in spreading disinformation on several occasions. In 1983, India and the Soviet Union both investigated secret tests but, due to lack of any scientific data, these statements were widely dismissed.[39]

In their book, The Nuclear Express, authors Thomas Reed and Danny Stillman also allege that the People's Republic of China allowed Pakistan to detonate a nuclear weapon at its Lop Nur test site in 1990, eight years before Pakistan held its first official weapons test.[40]

On September 9, 2004, it was reported by South Korean media that there had been a large explosion at the Chinese/North Korean border. This explosion left a crater visible by satellite and precipitated a large (2 mile diameter) mushroom cloud. The United States and South Korea quickly downplayed this, explaining it away as a forest fire that had nothing to do with the DPRK's nuclear weapons program.

Hitlers Bombe, a book published in German by the historian Rainer Karlsch in 2005, has alleged that there is evidence that Nazi Germany performed some sort of test of a "nuclear device" (a hybrid fusion device unlike any modern nuclear weapons) in March 1945, though the evidence for this has not yet been confirmed, and has been doubted by many historians.

Missiles and nuclear warheads have usually been tested separately, because testing them together is considered highly dangerous; they are certainly the most extreme type of live fire exercise. The only US live test of an operational missile was the following:

Frigate Bird: on May 6, 1962, a UGM-27 Polaris A-2 missile with a live 600 kt W47 warhead was launched from the USS Ethan Allen; it flew 190 km (120 mi), re-entered the atmosphere, and detonated at an altitude of 3.4 km (2.1 mi) over the South Pacific. The test was part of Operation Dominic I. Because the weapon was substantially modified before the test and because it flew a low-trajectory, low-range profile, the test was not deemed to have been as effective at dispelling doubt about the readiness and effectiveness of rocket-powered nuclear missiles as it was hoped to be.

Other live tests with the nuclear explosive delivered by rocket by the USA include:

On August 1, 1958, Redstone rocket launched nuclear test Teak that detonated at an altitude of 77.8 km (48.3 mi). On August 12, 1958, Redstone #CC51 launched nuclear test Orange to a detonation altitude of 43 km (27 mi). Both were part of Operation Hardtack I and had a yield of 3.75 Mt

Operation Argus: three tests above the South Atlantic Ocean, August 27, August 30, and September 6, 1958

On July 9, 1962, Thor missile launched a Mk4 reentry vehicle containing a W49 thermonuclear warhead to an altitude of 248 miles (400 km). The warhead detonated with a yield of 1.45 Mt. This was the Starfish Prime event of nuclear test operation Dominic-Fishbowl

In the Dominic-Fishbowl series in 1962: Checkmate, Bluegill, Kingfish and Tightrope

The 1957 test Plumbbob/John fired a small yield nuclear weapon on a Genie air-to-air rocket from a jet fighter.

The Soviet Union tested nuclear explosives on rockets as part of their development of a localised anti-ballistic missile system in the 1960s. Some of the Soviet nuclear tests with warheads delivered by rocket include: